~package-build~ allows a curator to publish an archive of Emacs packages. [[https://melpa.org][MELPA]] uses ~package-build~ and a few downstream projects are listed [[https://github.com/melpa/melpa/wiki/Downstream-Projects][here]].
The archive is generated from a set of recipes, which describe elisp projects and repositories from which to get them. The term "package" here is used to mean a specific version of a project that is prepared for download and installation. The recipe format is documented [[https://github.com/melpa/melpa#recipe-format][here]].